1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to a frame rate of recording and displaying an ultrasonic echogram.
2. Description of the Related Art
In operation of a conventional ultrasonic diagnostic apparatus such as shown in FIG. 1, an ultrasonic beam is transmitted from and received by a probe 1. The signal received by a transceiver 2 is processed by a received beam phase adjuster 3' and a detector/compressor 4' and written in a frame memory 6 and in a continuous image memory 7. The frame memory 6 stores the received image signal in the unit of frame, and the continuous image memory 7 continuously stores the received image signal indifferent to each frame. A signal read from the frame memory 6 or continuous image memory 7 is selected by a selector 8 and displayed on a display device 8. A data write operation for the memories 6 and 7 is performed in accordance with an address supplied from a memory write address circuit 14, whereas a data read operation for the memories is performed in accordance with an address supplied from a memory read address circuit 15. Operation timings for the whole circuit of the apparatus is controlled by a main clock generated by an oscillator 12. The main clock is supplied to a TV frame synchronizing signal generator 16 which in turn generates a TV frame synchronizing signal. By using this TV frame synchronizing signal, the operation timings of the transceiver 11, address circuits 14 and 15, and display device 10 are controlled.
In such a conventional apparatus, the control of transmitting/receiving ultrasonic beams and writing/reading image data to and from the memories 6 and 7 has been performed by using the TV frame synchronizing signal generated by the TV frame synchronizing signal generator 16 which is supplied with the main clock from the oscillator 12.
Specifically, an image signal has been picked up conventionally at a frame rate lower than the TV frame rate (30 frames/sec), for example, at 15 or 5 frames/sec, and displayed at 30 frames/sec.
Also in a conventional apparatus of a plural beam reception type, an image signal is picked up at a frame rate lower than the TV frame rate, and displayed at the TV frame rate.
An example of conventional image display will be described with reference to FIGS. 2A to 2C.
FIG. 2A is a timing chart of a TV frame synchronizing signal. The time period between two consecutive pulses corresponds to one frame (Fi). FIG. 2B is a timing chart explaining the operation of a frame memory wherein the image pickup frame rate is set to be equal to the TV frame rate. For example, the frame memory has two buffers each having a capacity of one frame. Data is written and read alternately between the two buffers. Specifically, while data is written in one of the two buffers, image data of one frame is read from the other buffer and displayed on the display device. FIG. 2C is a timing chart explaining the operation of a frame memory wherein the image pickup frame rate is set to a half of the TV frame rate. In this case, image data of one buffer is displayed twice synchronously with the TV frame synchronizing signal.
Conventional apparatuses are not intended to pick up an image at a frame rate higher than the TV frame rate and display it in slow motion.